Blood pressure in the living body is controlled mainly by the sympathetic nervous system and the balance of pressor and depressor systems. The renin-angiotensin system is a pressor system. In the renin-angiotensin system, renin acts on angiotensinogen to form angiotensin I which is subsequently converted into angiotensin II by the action of an angiotensin converting enzyme. Angiotensin II shows strong angiotonic activity and acts on the adrenal cortex to enhance secretion of aldosterone, thus increasing the blood pressure. Since angiotensin II exerts its function through the angiotensin II receptor located on the cell membrane, its antagonist can be used, in addition to an angiotensin converting enzyme inhibitor, as a therapeutic agent for the treatment of hypertension caused by angiotensin II.
Angiotensin II antagonist peptides such as saralasin are known in the art. However, peptides are not effective when administered orally. Recently, non-peptide angiotensin II antagonists have been reported, for example, in JP-A-56-71074, PCT Application published in Japan No. 3-501020, JP-A-3-95181, JP-A-3-236377 and JP-A-3-271288, and their efficacy by oral administration has been confirmed. (The term "JP-A" as used herein means an "unexamined published Japanese patent application")